Sr₂[B₅O₈(OH)]₂ ⋅ [B(OH)₃] ⋅ H₂O: A Strontium Borate That Shows Deep-Ultraviolet-Transparent Nonlinear Optical...

Area of Science:

• Solid-state chemistry
• Materials science
• Crystallography
• Nonlinear optics

Background:

• Strontium borates are a class of inorganic compounds with diverse structures and properties.
• Noncentrosymmetric crystals are crucial for nonlinear optical (NLO) applications.
• Veatchite is a naturally occurring strontium borate mineral, with known polymorphs.

Purpose of the Study:

• To synthesize and characterize a new noncentrosymmetric strontium borate compound.
• To investigate the crystal structure and potential nonlinear optical properties of the new material.
• To compare the synthesized compound with known natural phases of veatchite.

Main Methods:

• Hydrothermal synthesis was employed to obtain the single crystals of P1-Sr₂[B₅O₈(OH)]₂⋅[B(OH)₃]⋅H₂O.
• Crystal structure was determined.
• Nonlinear optical properties, including second-harmonic-generation (SHG) intensity and phase-matching ability, were evaluated. Density functional theory (DFT) calculations were performed to understand the origin of NLO properties.

Main Results:

• A new noncentrosymmetric strontium borate, P1-Sr₂[B₅O₈(OH)]₂⋅[B(OH)₃]⋅H₂O, was successfully synthesized.
• The compound exhibits a layered structure with 9-ring windows in the ab plane, with Sr²⁺ cations, boric acid, and water molecules in the voids.
• It demonstrates a strong deep-ultraviolet transparency (cutoff edge < 190 nm), a phase-matchable SHG intensity 1.7 times that of KH₂PO₄ (KDP), and DFT calculations indicate B-O units are responsible for the NLO property.

Conclusions:

• P1-Sr₂[B₅O₈(OH)]₂⋅[B(OH)₃]⋅H₂O represents the first synthetic phase of veatchite.
• This novel strontium borate is a promising candidate for deep-ultraviolet nonlinear optical applications.
• The study highlights the potential of exploring new strontium borate materials for advanced optical devices.